In a randomized, double-blind, prospective trial we compared the efficacy of pre-treatment with nitrous oxide (with or without premixed lignocaine in propofol) for the prevention of propofol-induced pain. Ninety consecutive patients were recruited in the study and divided into three groups of 30 each, who received either 50% nitrous oxide in oxygen along with lignocaine 40 mg mixed in 1% propofol 20 ml (Group NL), 50% nitrous oxide in oxygen without lignocaine in propofol (Group N), and 50% oxygen in air with lignocaine mixed in propofol 40 mg (Group L). Pain scores were graded on a four point verbal rating scale (0-3). Eighty-nine patients completed the study while one patient developed excitement, agitation and tremor during nitrous oxide in oxygen inhalation. Eleven patients (36.7%) complained of pain in the group L compared to 7 (23.3%), and 1 (3.3%), in groups N and NL respectively [group NL vs group L (P<0.001) and group NL vs N (P<0.001)]. There was no statistical difference observed between group N and group L. Inhalation of 50% nitrous oxide reduces pain on propofol injection. The combination of 50% nitrous oxide and lignocaine mixed with propofol was the most effective treatment.

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